Diamond is an extremely sought after material due to its combination of extreme hardness, chemical inertness, low electrical and high thermal conductivities, wide optical transparency, and other unique properties [Wilks, E.; Wilks, J. Properties and Applications of Diamond, Butterworth, Oxford, England, 1997; Pierson, H. O. Handbook of Carbon, Graphite, Diamond and Fullerenes, Noyes Publ. Park Ridge, N.J., USA, 1993]. Diverse applications of diamond materials have been facilitated by the mid 1950s discovery and subsequent development of processes for large-scale production of synthetic diamonds [Pierson, H. O. Handbook of Carbon, Graphite, Diamond and Fullerenes, Noyes Publ. Park Ridge, N.J., USA, 1993]. These industrial processes primarily employ high pressure-high temperature technologies to produce single-crystalline diamonds, while on the laboratory scale, methods of physical and chemical vapor deposition of polycrystalline diamond films are commonly used. These diamond materials have been traditionally applied as abrasives and cutting tools and also as substrates in microelectronics.
In recent years, a number of synthetic methods for the preparation of nanocrystalline diamond, “nanodiamond” (ND), in the form of films and powders, have been developed [Shenderova et al., Critical Reviews in Solid State and Materials Sciences 2002, 27, 227; Dolmatov, Russian Chemical Reviews 2001, 70, 607]. Particularly, detonation synthesis, from powerful explosive mixtures [Greiner et al., Nature, 1988, 333, 440; Vereschagin et al., Dia. Relat. Mater. 1993, 3, 160; Kuznetsov et al., Carbon, 1994, 32, 873] has made such nanodiamond powder commercially available in ton quantities which has enabled many engineering applications and has expanded the application scope of diamond [Dolmatov, Russian Chemical Reviews 2001, 70, 607].
Nanodiamond (ND) powders prepared by explosive techniques present a novel class of nanomaterials possessing unique surface properties. Due to the very small particle size (2-10 nm), a larger percentage of atoms in nanodiamonds contribute to the defect sites on grain boundaries than in single crystal natural or microcrystalline synthetic diamonds. For example, in individual 4.3 nm spherical particles of ND comprising about 7200 carbon atoms, nearly 1100 atoms are located at the surface [Shenderova et al., Critical Reviews in Solid State and Materials Sciences 2002, 27, 227]. For this reason, the surface modifications of the nanosize diamond grains can affect the bulk properties of this material more strongly than those of micro- and macroscale diamonds. For example, nanodiamond powders can form good abrasive pastes and suspensions for high-precision polishing; nanodiamond-polymer composites are applied for manufacturing aircraft, cars and ships, as well as in hard and wear-resistant surface coatings. They are considered potential medical agents due to their high adsorption capacity, high specific surface area, and chemical inertness [Shenderova et al., Critical Reviews in Solid State and Materials Sciences 2002, 27, 227; Dolmatov, Russian Chemical Reviews 2001, 70, 607]. Applications of nanodiamond thin films have been demonstrated in the fabrication of cold cathodes, field emission displays [Alimova et al., J. Vac. Sci. Technol. B 1999, 17, 715; Show et al., Chem. Mater. 2003, 15, 879; Choi et al., Appl. Phys. Lett. 1996, 68, 720; Ralchenko et al., Diamond Relat. Mater. 1999, 8, 1496; Jiang et al., J. Cryst. Growth 2002, 236, 577], nanomechanical and nanoelectromechanical resonant structures (NEMS) [Wang et al., Proc. of The Fifteenth IEEE Internat. Conf. On Micro Electromechanical Systems, 2002, 657; Sekaric et al., Appl. Phys. Lett. 2002, 81, 4455; Philip et al., J. Appl. Phys. 2003, 93, 2164], and were suggested for the design of biosensors as stable biologically active substrates after DNA-modification [Yang et al., Nature Mater. 2002, 1, 253].
In order to minimize surface energy, individual ND particles (crystallites) of 4-6 nm size structurally self-organize into clusters or primary aggregates of 20-30 mm size. These, in turn, form larger weakly bonded secondary aggregates ranging from hundreds of nanometers to micron sizes. This agglomeration is likely facilitated by surface functional groups, such as —OH, —COOH, —SO3H, and —NH2, which are created along with other functionalities by chemical treatment processing of detonation-synthesized ND [Shenderova et al., Critical Reviews in Solid State and Materials Sciences 2002, 27, 227; Jiang et al., J. Chem. Soc., Faraday Trans. 1996, 92, 3401] and participate in the formation of hydrogen bonds between nanodiamond clusters. However, for advanced applications of ND powder (e.g., in higher precision polishing compositions, nanoengineered electronic devices, polymer and ceramic composites, and bio-medical systems), the reduction of aggregate sizes to below 200 nm, and ultimately even to single clusters or particles, and the availability of specific functional groups on the surface is highly desirable. These functional groups can also serve as binding sites for covalent integration of ND into polymer structures and provide for improved solubility of ND powder in common solvents. Surface modification of the ND powder particles through a selective surface chemistry should be instrumental in approaching these goals.
Diamond surface modification has been studied during the past decade [Yang et al., Nature Mater. 2002, 1, 253; Hamers et al., Acc. Chem. Res. 2000, 33, 617; Bent et al., Surf. Sci. 2002, 500, 879; Hukka et al., J. Phys. Chem. 1994, 98, 12420; Hovis et al., J. Am. Chem. Soc. 2000, 122, 732; Wang et al., J. Am. Chem. Soc. 2000, 122, 744; Fitzgerald et al., J. Am. Chem. Soc. 2000, 122, 12334; Hossain et al., Jpn. J. Appl. Phys. 1999, 38, L1496; Miller et al., Langmuir 1996, 12, 5809; Smentkowski et al., Science 1996, 271, 193; Kim et al., J. Phys. Chem. B 1998, 102, 9290; Nakamura et al., Chem. Commun. 2003, 900] and fluorination has been regarded as an efficient way to modify and control diamond's surface properties [Smentkowski et al., Science 1996, 271, 193; Ando et al., Diamond Relat. Mater. 1996, 5, 1021; Kealey et al., J. Mater. Chem. 2001, 11, 879; Ando et al., J. Chem. Soc., Faraday Trans. 1993, 89, 3105; Touhara et al., Carbon 2000, 38, 241; Ferro et al., J. Phys. Chem. B 2003, 107, 7567; Ferro et al., Anal. Chem. 2003, 75, 7040]. However, all previous work has been done either on larger size (micronscale) polycrystalline diamond [Miller et al., Langmuir 1996, 12, 5809; Nakamura et al., Chem. Commun. 2003, 900; Ando et al., Diamond Relat. Mater. 1996, 5, 1021; Kealey et al., Mater. Chem. 2001, 11, 879] or on thin films [Yang et al., Nature Mater. 2002, 1, 253; Hamers et al., Acc. Chem. Res. 2000, 33, 617; Bent, Surf. Sci. 2002, 500, 879; Hukka et al., J. Phys. Chem. 1994, 98, 12420; Hovis et al., J. Am. Chem. Soc. 2000, 122, 732; Wang et al., J. Am. Chem. Soc. 2000, 122, 744; Fitzgerald et al., J. Am. Chem. Soc. 2000, 122, 12334. Hossain et al., Jpn. J. Appl. Phys. 1999, 38, L1496; Smentkowski et al., Science 1996, 271, 193. Kim et al., J. Phys. Chem. B 1998, 102, 9290; Ando et al., J. Chem. Soc., Faraday Trans. 1993, 89, 3105] grown in vacuum chambers, and no further chemistry (e.g., chemistry utilizing the C—F bond reactivity in particular) was pursued after fluorination.
In view of the foregoing, functionalized nanodiamond powder will likely extend the utility of nanodiamond powder, and methods of making such functionalized nanodiamond powder will be in great demand.